Summary/Abstract Age-related decline in cognitive functioning is one of the most pressing concerns our country faces. In the context of this important societal challenge, we now know that cognitive functioning is reliably associated with aspects of the person (i.e., individual differences in personality traits) as well as the key social contexts in which the person is embedded (i.e., the quality and nature of adults' interpersonal experiences). That key intra- and interpersonal resources are reliably associated with cognitive status is now not in dispute. Nevertheless, the degree to which these associations emerge from environmentally mediated processes amenable to intervention remains largely unknown because existing research cannot rule out the possibility that some of these associations might reflect the impact of confounds, including especially evocative genetic processes, that produce correlations between personality/interpersonal experiences and cognitive health. We propose to use an innovative co-twin control design to rule out potential genetic and family background confounds. This will allow us to identify environmentally mediated connections linking both personality and interpersonal experiences in advancing age with cognitive functioning, ultimately positioning our program of research to contribute to the study of Alzheimer's Disease and its related Dementias. We will pursue this topic in the context of a genetically informed research design. Though this has never before been done, it is critical in properly targeting interventions to improve cognitive functioning among older adults. More specifically, we will study whether the relation between individual/interpersonal differences and cognitive health is environmentally mediated by working with participants in the Minnesota Twin Registry (MTR) now in late life (800 twin pairs), a group that completed an assessment of personality previously when they were ~38 years old). The acquisition of new measures of cognitive functioning from the MTR will allow us to address our specific aims: (Aim 1) Obtain baseline data on cognitive functioning and activities of daily living (ADLs) from twin participants in our parent R01 project; and (Aim 2) Perform a preliminary study of the etiology of associations linking personality, relationship quality, and incipient cognitive decline.